Circularly polarizing plate

ABSTRACT

Provided is a circularly polarizing plate that is excellent in antireflection characteristic, and that can be produced at low cost. The circularly polarizing plate of the present invention includes in the stated order: a polarizer; a retardation layer (20a) configured to function as a λ/4 plate; and a colored layer, wherein an angle formed by an absorption axis of the polarizer and a slow axis of the retardation layer (20a) is from 35° to 55°, wherein the colored layer has an absorption peak in a wavelength band in a range of from 580 nm to 610 nm, and wherein the colored layer contains a compound X represented by the general formula (I) or the general formula (II).

TECHNICAL FIELD

The present invention related to a circularly polarizing plate.

BACKGROUND ART

In recent years, the number of opportunities for a smart device typifiedby a smartphone and a display apparatus, such as a digital signage or awindow display, to be used under strong ambient light has beenincreasing. Along with the increase, a problem, such as ambient lightreflection or background reflection, due to the display apparatus itselfor a reflector used in the display apparatus, such as a touch panelportion, a glass substrate, or metal wiring, has been occurring. In viewof the foregoing, it has been known that such phenomenon is prevented byarranging a circularly polarizing plate including a λ/4 plate on theviewer side of the apparatus. A circularly polarizing plate obtained asdescribed below has been known as a general circularly polarizing plate.A retardation film (typically a λ/4 plate) typified by a cycloolefin(COP)-based resin film is laminated so that its slow axis may form anangle of about 45° with respect to the absorption axis of a polarizer.The retardation film made of a COP-based resin has been known to havesuch a so-called flat wavelength dispersion characteristic that itsretardation value does not depend on the wavelength of measurement lightand is substantially constant. When a circularly polarizing plateincluding a retardation film having such flat wavelength dispersioncharacteristic is used in a display apparatus, a problem in that anexcellent reflection hue is not obtained occurs.

To solve such problem as described above, there has been proposed acircularly polarizing plate including a retardation film having suchso-called reverse wavelength dispersion dependency (reverse wavelengthdispersion characteristic) that its retardation value increases inaccordance with an increase in wavelength of measurement light (e.g.,Patent Literature 1). However, the use of the retardation film having areverse wavelength dispersion characteristic is disadvantageous in termsof cost. In addition, when the film is applied to a reflector having ahigh reflectance, a problem in that it is particularly difficult toadjust the hue of the reflector occurs.

CITATION LIST Patent Literature

[PTL 1] JP 2006-171235 A

SUMMARY OF INVENTION Technical Problem

The present invention has been made to solve the conventional problems,and a primary object of the present invention is to provide a circularlypolarizing plate that is excellent in antireflection characteristic,that has a neutral reflection hue, and that can be produced at low cost.

Solution to Problem

According to one embodiment of the present invention, there is provideda circularly polarizing plate, including in the stated order: apolarizer; a retardation layer “a” configured to function as a λ/4plate; and a colored layer, wherein an angle formed by an absorptionaxis of the polarizer and a slow axis of the retardation layer “a” isfrom 35° to 55°, wherein the colored layer has an absorption peak in awavelength band in a range of from 580 nm to 610 nm, and wherein thecolored layer contains a compound X represented by the following generalformula (I) or general formula (II):

in the formula (I),

R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ each independently represent ahydrogen atom, a halogen atom, a substituted or unsubstituted alkylgroup having 1 or more and 20 or less carbon atoms, a substituentrepresented by the formula (a), or a substituent represented by theformula (b),

R₁ and R₂ form a saturated cyclic skeleton including 5 or 6 carbonatoms, and R₃, R₄, R₅, R₆, R₇, and R₈ each independently represent ahydrogen atom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b),

R₂ and R₃ form a saturated cyclic skeleton including 5 to 7 carbonatoms, and R₁, R₄, R₅, R₆, R₇, and R₈ each independently represent ahydrogen atom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b),

R₅ and R₆ form a saturated cyclic skeleton including 5 or 6 carbonatoms, and R₁, R₂, R₃, R₄, R₇, and R₈ each independently represent ahydrogen atom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b),

R₆ and R₇ form a saturated cyclic skeleton including 5 to 7 carbonatoms, and R₁, R₂, R₃, R₄, R₅, and R₈ each independently represent ahydrogen atom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b),

R₁ and R₂ form a saturated cyclic skeleton including 5 or 6 carbonatoms, R₅ and R₆ form a saturated cyclic skeleton including 5 or 6carbon atoms, and R₃, R₄, R₇, and R₈ each independently represent ahydrogen atom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b), or

R₂ and R₃ form a saturated cyclic skeleton including 5 to 7 carbonatoms, R₆ and R₇ form a saturated cyclic skeleton including 5 to 7carbon atoms, and R₁, R₄, R₅, and R₈ each independently represent ahydrogen atom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b); and

in the formula (II), R₄ and R₈ each independently represent a hydrogenatom, or a substituted or unsubstituted alkyl group having 1 or more and20 or less carbon atoms.

In one embodiment, a laminate including the polarizer and the coloredlayer has a polarization degree of 99.9% or more.

In one embodiment, the circularly polarizing plate further includes aretardation layer “b” configured to function as a λ/2 plate between thepolarizer and the retardation layer “a” configured to function as a λ/4plate, wherein the angle formed by the absorption axis of the polarizerand the slow axis of the retardation layer “a” is from 65° to 85°, andwherein an angle formed by the absorption axis of the polarizer and aslow axis of the retardation layer “b” is from 10° to 20°.

In one embodiment, the colored layer further has an absorption peak in awavelength band in a range of from 440 nm to 510 nm.

In one embodiment, the retardation layer “a” configured to function as aλ/4 plate has a ratio Re(450)/Re(550) of 0.5 or more and less than 1.0,and the retardation layer “a” has an Nz coefficient of from 0.3 to 0.7.

According to another embodiment of the present invention, there isprovided an image display apparatus. The image display apparatusincludes the circularly polarizing plate.

In one embodiment, the image display apparatus further includes an imagedisplay panel, wherein the image display panel has a visible lightreflectance of 20% or more.

Advantageous Effects of Invention

According to the present invention, the circularly polarizing plateexcellent in antireflection characteristic can be obtained by formingthe colored layer. In addition, the circularly polarizing plate of thepresent invention can output light having a neutral hue through theadjustment of its reflection hue by appropriate setting of theabsorption wavelength of the colored layer. Further, the use of thecircularly polarizing plate of the present invention can widen the colorgamut of the image display apparatus while preventing a reduction inbrightness thereof.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view of a circularly polarizing plateaccording to one embodiment of the present invention.

FIG. 2 is a schematic sectional view of a circularly polarizing plateaccording to another embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Now, preferred embodiments of the present invention are described.However, the present invention is not limited to these embodiments.

DEFINITIONS OF TERMS AND SYMBOLS

The definitions of terms and symbols in this description are asdescribed below.

(1) Refractive Index (Nx, Ny, or Nz)

The symbol “nx” represents a refractive index in the direction in whicha refractive index in a plane becomes maximum (i.e., a slow axisdirection), the symbol “ny” represents a refractive index in thedirection perpendicular to the slow axis in the plane (i.e., a fast axisdirection), and the symbol “nz” represents a thickness directionrefractive index.

(2) In-plane Retardation (Re)

The symbol “Re(λ)” represents an in-plane retardation measured withlight having a wavelength of λ nm at 23° C. For example, the symbol“Re(550)” represents an in-plane retardation measured with light havinga wavelength of 550 nm at 23° C. When the thickness of a layer (film) isrepresented by d (nm), the Re(λ) is determined from the equation“Re=(nx−ny)×d”.

(3) Thickness Direction Retardation (Rth)

The symbol “Rth(λ)” represents a thickness direction retardationmeasured with light having a wavelength of λ nm at 23° C. For example,the symbol “Rth(550)” represents a thickness direction retardationmeasured with light having a wavelength of 550 nm at 23° C. When thethickness of a layer (film) is represented by d (nm), the Rth(λ) isdetermined from the equation “Rth=(nx−nz)×d”.

(4) Nz Coefficient

An Nz coefficient is determined from the equation “Nz=Rth/Re”.

A. Circularly Polarizing Plate

A-1. Overall Configuration of Circularly Polarizing Plate

FIG. 1 is a schematic sectional view of a circularly polarizing plateaccording to one embodiment of the present invention. A circularlypolarizing plate 100 of this embodiment includes a polarizer 10, aretardation layer 20 a, and a colored layer 30 in the stated order. Theretardation layer 20 a may function as a λ/4 plate. The circularlypolarizing plate 100 may be used so that the colored layer 30 may be ona reflector (e.g., an image display panel, such as a liquid crystaldisplay panel or an organic EL panel) side, and the polarizer 10 may beon a viewer side. In one embodiment, the circularly polarizing plate 100includes a protective film 40 on the surface of the polarizer 10opposite to the retardation layer 20 a. The protective film 40 may beomitted in accordance with, for example, an application or theconfiguration of an image display apparatus including the circularlypolarizing plate. In addition, the circularly polarizing plate mayinclude another protective film (also referred to as “inner protectivefilm”: not shown) between the polarizer and the retardation layer. Inthe illustrated example, the inner protective film is omitted. In thiscase, the retardation layer 20 a may also function as an innerprotective film. With such configuration, further thinning of thecircularly polarizing plate can be achieved.

In this embodiment, an angle formed by the absorption axis of thepolarizer 10 and the slow axis of the retardation layer 20 a is from 35°to 55°, preferably from 38° to 52°, more preferably from 40° to 50°,still more preferably from 42° to 48°, particularly preferably from 44°to 46°. When the angle falls within such range, a desired circularpolarization function can be achieved. When reference is made to anangle in this description, the angle comprehends angles in both ofclockwise and counterclockwise directions unless otherwise stated.

The circularly polarizing plate of the present invention may typicallyfunction as an antireflection film by being arranged on the viewer sideof an image display apparatus. The circularly polarizing plate of thepresent invention exhibits an excellent antireflection function whilebeing suppressed in visible light transmittance reduction (i.e., abrightness reduction) because the circularly polarizing plate includesthe colored layer, and the colored layer contains a specific coloringmatter to be described later (coloring matter represented by the generalformula (I) or (II)) to absorb light having a specific wavelength. Evenwhen the circularly polarizing plate of the present invention is appliedto an image display apparatus including a reflector having a highreflectance (e.g., a reflectance of 20% or more), reflected light fromthe reflector can be sufficiently shielded. In addition, when thecolored layer selectively absorbs light in a specific wavelength range(from 580 nm to 610 nm) and is suppressed in unneeded absorption in awavelength range except the specific wavelength range, a circularlypolarizing plate having the following features can be obtained: itsreflection hue can be appropriately adjusted; and the circularlypolarizing plate can contribute to the widening of the color gamut of animage display apparatus, and to an improvement in brightness thereof.According to the present invention, the color gamut of the image displayapparatus can be significantly widened without the use of a high-costtechnology (an organic EL technology or a quantum dot technology). Inother words, when a liquid crystal display panel is combined with thecircularly polarizing plate of the present invention, color gamutwidening comparable to (or comparable to or more than) that of an imagedisplay apparatus formed by the organic EL technology or the quantum dottechnology can be achieved at low cost. Needless to say, further colorgamut widening can be achieved by combining the circularly polarizingplate of the present invention with the organic EL technology, thequantum dot technology, or the like.

FIG. 2 is a schematic sectional view of a circularly polarizing plateaccording to another embodiment of the present invention. A circularlypolarizing plate 100′ of this embodiment further includes anotherretardation layer 20 b between the polarizer 10 and the retardationlayer 20 a (λ/4 plate). The other retardation layer 20 b functions as aλ/2 plate. In this description, for convenience, the retardation layer20 a (λ/4 plate) is sometimes referred to as “first retardation layer”,and the other retardation layer 20 b (λ/2 plate) is sometimes referredto as “second retardation layer”. The circularly polarizing plate 100′of the illustrated example includes the protective film 40 on the sideof the polarizer 10 opposite to the other retardation layer 20 b. Inaddition, the circularly polarizing plate may include another protectivefilm (also referred to as “inner protective film”: not shown) betweenthe polarizer and the retardation layer 20 a. In the illustratedexample, the inner protective film is omitted. In this case, the otherretardation layer (second retardation layer) 20 b may also function asan inner protective film.

In this embodiment, the angle formed by the absorption axis of thepolarizer 10 and the slow axis of the first retardation layer 20 a ispreferably from 65° to 85°, more preferably from 72° to 78°, still morepreferably about 75°. Further, an angle formed by the absorption axis ofthe polarizer 10 and the slow axis of the second retardation layer 20 bis preferably from 10° to 20°, more preferably from 13° to 17°, stillmore preferably about 15°. When the two retardation layers are arrangedat such axial angles as described above, a circularly polarizing platehaving an extremely excellent circular polarization characteristic(consequently, an extremely excellent antireflection characteristic) ina wide band can be obtained.

In one embodiment, the circularly polarizing plate of the presentinvention is free of any other retardation layer except the retardationlayer that may function as a λ/4 plate and the retardation layer thatmay function as a λ/2 plate. The circularly polarizing plate of thepresent invention can be produced at low cost because the circularlypolarizing plate may have an excellent antireflection function, anexcellent hue-adjusting function, and an excellent color gamut-wideningfunction without including any other retardation layer.

The polarization degree of a laminate “x” including the polarizer andthe colored layer is preferably 99.9% or more, more preferably 99.95% ormore, still more preferably 99.99% or more. The laminate “x” is obtainedby: producing the same polarizer and colored layer as the polarizer andthe colored layer forming the circularly polarizing plate; andlaminating the polarizer and the colored layer. The laminate “x” mayinclude any other layer (e.g., a protective film) that does not affectthe polarization degree. In one embodiment, when a colored layer havinga low haze value is formed, the depolarization of light passing thecolored layer is suppressed, and hence the polarization degree of thelaminate “x” can be increased. The use of the polarizer and the coloredlayer forming the laminate “x” having a high polarization degree canprovide a circularly polarizing plate that exhibits an excellentantireflection function. The upper limit value of the polarizationdegree of the laminate “x” is, for example, 99.9990. The polarizationdegree of the laminate “x” may be determined from the following equationby measuring the single layer transmittance (Ts), parallel transmittance(Tp), and cross transmittance (Tc) of the laminate “x” with anultraviolet-visible spectrophotometer (manufactured by JASCOCorporation, product name: “V-7000 SERIES”).

Polarization degree(P) (%)={(Tp−Tc)/(Tp+Tc)}^(1/2)×100

The parallel transmittance (Tp) and the cross transmittance (Tc) aremeasured by causing polarized light to enter from the colored layer sideof the laminate “x”. In addition, the Ts, the Tp, and the Tc are Yvalues measured with the two-degree field of view (C light source) ofJIS Z 8701 and subjected to visibility correction.

In one embodiment, the outermost surface (e.g., a surface serving as aviewer side) of the circularly polarizing plate is subjected to alow-reflection treatment, and hence the circularly polarizing plateincludes a low-reflection-treated layer on the outermost surface.Examples of the low-reflection treatment include: a method includingbonding an antireflection film to the outermost surface; a methodincluding forming a thin film from, for example, a low-refractive indexresin provided with voids, such as a fluorine resin or hollow silica,through a wet process, such as coating or application (e.g., PatentLiterature: JP 2013-64934 A); and a method including providing amultilayer antireflection film through the combination of a dry processand the wet process, such as coating or application (e.g., PatentLiterature: JP 2002-243906 A).

A-2. Polarizer and Protective Film

Any appropriate polarizer is used as the polarizer. Examples thereofinclude polyene-based alignment films, such as: a product obtained bycausing a hydrophilic polymer film, such as a polyvinyl alcohol-basedfilm, a partially formalized polyvinyl alcohol-based film, or anethylene-vinyl acetate copolymer-based partially saponified film, toadsorb a dichroic substance, such as iodine or a dichroic dye, anduniaxially stretching the resultant; a dehydration-treated product ofpolyvinyl alcohol; and a dehydrochlorination-treated product ofpolyvinyl chloride. Of those, a polarizer obtained by causing thepolyvinyl alcohol-based film to adsorb the dichroic substance, such asiodine, and uniaxially stretching the resultant is particularlypreferred because of its high polarization dichroic ratio. The thicknessof the polarizer is preferably from 0.5 μm to 80 μm.

The polarizer obtained by causing the polyvinyl alcohol-based film toadsorb iodine and uniaxially stretching the resultant is typicallyproduced by: immersing polyvinyl alcohol in an aqueous solution ofiodine to dye the polyvinyl alcohol; and stretching the dyed polyvinylalcohol so that the polyvinyl alcohol may have a length 3 to 7 times aslong as its original length. The stretching may be performed after thedyeing, the stretching may be performed while the dyeing is performed,or the dyeing may be performed after the stretching. The polarizer isproduced through a treatment, such as swelling, cross-linking,adjustment, water washing, or drying, in addition to the stretching andthe dyeing. For example, when the polyvinyl alcohol-based film is washedwith water by being immersed in the water before the dyeing,contamination and an antiblocking agent on the surface of the polyvinylalcohol-based film can be washed off. Moreover, the polyvinylalcohol-based film can be swollen to prevent its dyeing unevenness orthe like. The polyvinyl alcohol-based film may be a single-layer film(typical film obtained by film forming), or may be a polyvinylalcohol-based resin layer applied and formed onto a resin substrate. Atechnology involving producing a polarizer from the single-layerpolyvinyl alcohol-based film is well known in the art. A technologyinvolving producing a polarizer from the polyvinyl alcohol-based resinlayer applied and formed onto the resin substrate is described in, forexample, JP 2009-098653 A.

The polarizer preferably shows absorption dichroism at any wavelength inthe wavelength range of from 380 nm to 780 nm. The single layertransmittance of the polarizer is preferably from 38% to 45.5%, morepreferably from 40% to 45%.

The polarization degree of the polarizer is preferably 99.9% or more,more preferably 99.95% or more. When the polarization degree fallswithin such ranges, a circularly polarizing plate that exhibits adesired circular polarization function and that is excellent inantireflection characteristic can be obtained.

Any appropriate film is used as the protective film. Specific examplesof a material serving as a main component of such film include:cellulose-based resins, such as triacetyl cellulose (TAC); andtransparent resins, such as (meth)acrylic, polyester-based, polyvinylalcohol-based, polycarbonate-based, polyamide-based, polyimide-based,polyether sulfone-based, polysulfone-based, polystyrene-based,polynorbornene-based, polyolefin-based, and acetate-based resins.Examples thereof also include thermosetting resins or UV-curable resins,such as acrylic, urethane-based, acrylic urethane-based, epoxy-based,and silicone-based resins. Examples thereof also include glassypolymers, such as a siloxane-based polymer. In addition, a polymer filmdescribed in JP 2001-343529 A (WO 01/37007 A1) may also be used. Forexample, a resin composition containing a thermoplastic resin having asubstituted or unsubstituted imide group in a side chain thereof, and athermoplastic resin having a substituted or unsubstituted phenyl groupand a nitrile group in side chains thereof may be used as a material forthe film, and the resin composition is, for example, a resin compositionincluding: an alternating copolymer formed of isobutene andN-methylmaleimide; and an acrylonitrile-styrene copolymer. The polymerfilm may be, for example, an extrusion molded product of the resincomposition. Any appropriate pressure-sensitive adhesive layer oradhesive layer is used in the lamination of the polarizer and theprotective film. The pressure-sensitive adhesive layer is typicallyformed of an acrylic pressure-sensitive adhesive. The adhesive layer istypically formed of a polyvinyl alcohol-based adhesive.

A-3. First Retardation Layer (Retardation Layer configured to functionas λ/4 Plate)

As described above, the first retardation layer may function as a λ/4plate. The in-plane retardation Re(550) of such first retardation layeris from 100 nm to 180 nm, preferably from 110 nm to 170 nm, morepreferably from 120 nm to 160 nm, particularly preferably from 135 nm to155 nm. The first retardation layer typically has a refractive indexellipsoid of nx>ny=nz or nx>ny>nz. For example, the equation “ny=nz” asused herein comprehends not only a case in which the ny and the nz arestrictly equal to each other but also a case in which the ny and the nzare substantially equal to each other. The Nz coefficient of the firstretardation layer is, for example, from 0.9 to 2, preferably from 1 to1.5, more preferably from 1 to 1.3.

The thickness of the first retardation layer may be set so that thelayer may most appropriately function as a λ/4 plate. In other words,the thickness may be set so that a desired in-plane retardation may beobtained. Specifically, the thickness is preferably from 10 μm to 80 μm,more preferably from 10 μm to 60 μm, most preferably from 30 μm to 50μm.

The first retardation layer may show such a reverse wavelengthdispersion characteristic that its retardation value increases inaccordance with an increase in wavelength of measurement light, may showsuch a positive wavelength dispersion characteristic that theretardation value reduces in accordance with an increase in wavelengthof the measurement light, or may show such a flat wavelength dispersioncharacteristic that the retardation value remains substantiallyunchanged irrespective of the wavelength of the measurement light.

In one embodiment, the first retardation layer shows a flat wavelengthdispersion characteristic. The adoption of the first retardation layershowing a flat wavelength dispersion characteristic can achieve anexcellent antireflection characteristic and an excellent reflection huein an oblique direction. In addition, the circularly polarizing plate ofthe present invention can achieve an excellent reflection hue eventhrough the use of the first retardation layer showing a flat wavelengthdispersion characteristic. The circularly polarizing plate using thefirst retardation layer showing a flat wavelength dispersioncharacteristic is advantageous in terms of cost. In this embodiment, theratio Re(450)/Re(550) of the first retardation layer is preferably from0.99 to 1.03, and the ratio Re(650)/Re(550) thereof is preferably from0.98 to 1.02.

In another embodiment, the first retardation layer shows a reversewavelength dispersion characteristic. The adoption of the firstretardation layer showing a reverse wavelength dispersion characteristiccan improve a reflection hue in a front direction. In addition, theadoption of the first retardation layer showing a reverse wavelengthdispersion characteristic can improve any other characteristic (e.g., abrightness) while maintaining a practical reflection hue. In thisembodiment, the ratio Re(450)/Re(550) of the first retardation layer ispreferably 0.5 or more and less than 1.0, more preferably from 0.7 to0.95. In addition, the ratio Re(650)/Re(550) of the first retardationlayer is preferably more than 1 and 1.2 or less, more preferably from1.01 to 1.15. In this embodiment, the Nz coefficient of the firstretardation layer is preferably from 0.3 to 0.7, more preferably from0.4 to 0.6, still more preferably from 0.45 to 0.55, particularlypreferably about 0.5. When the Nz coefficient falls within such ranges,a more excellent reflection hue can be achieved.

The λ/4 plate is preferably a stretched film of a polymer film.Specifically, the λ/4 plate is obtained by appropriately selecting thekind of the polymer and a stretching treatment (e.g., a stretchingmethod, a stretching temperature, a stretching ratio, or a stretchingdirection).

Any appropriate resin is used as a resin forming the polymer film.Specific examples thereof include resins each forming a positivebirefringent film, such as a cycloolefin-based resin, such aspolynorbornene, a polycarbonate-based resin, a cellulose-based resin, apolyvinyl alcohol-based resin, and a polysulfone-based resin. Of those,a norbornene-based resin and a polycarbonate-based resin are preferred.Details about the resin forming the polymer film are described in, forexample, JP 2014-010291 A, the description of which is incorporatedherein by reference.

The polynorbornene refers to a (co)polymer obtained by using anorbornene-based monomer having a norbornene ring as part or theentirety of starting materials (monomers). Examples of thenorbornene-based monomer include: norbornene, alkyl and/or alkylidenesubstituted products thereof, such as 5-methyl-2-norbornene,5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, and5-ethylidene-2-norbornene, and polar group (e.g., halogen) substitutedproducts thereof; dicyclopentadiene and 2,3-dihydrodicyclopentadiene;dimethanooctahydronaphthalene, alkyl and/or alkylidene substitutedproducts thereof, and polar group (e.g., halogen) substituted productsthereof, such as6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene,6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene,6-ethylidene-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene,6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene,6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene,6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, and6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene;and trimers or tetramers of cyclopentadiene, such as4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzoindene and4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentaanthracene.

Various products are commercially available as the polynorbornene.Specific examples thereof include: products available under the productnames “ZEONEX” and “ZEONOR” from Zeon Corporation; a product availableunder the product name “Arton” from JSR Corporation; a product availableunder the product name “TOPAS” from TICONA; and a product availableunder the product name “APEL” from Mitsui Chemicals, Inc.

An aromatic polycarbonate is preferably used as the polycarbonate-basedresin. The aromatic polycarbonate may be typically obtained by areaction between a carbonate precursor and an aromatic dihydric phenolcompound. Specific examples of the carbonate precursor include phosgene,a bischloroformate of a dihydric phenol, diphenyl carbonate, di-p-tolylcarbonate, phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate, anddinaphthyl carbonate. Of those, phosgene and diphenyl carbonate arepreferred. Specific examples of the aromatic dihydric phenol compoundinclude 2,2-bis(4-hydroxyphenyl)propane,2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane,bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane,2,2-bis(4-hydroxyphenyl)butane,2,2-bis(4-hydroxy-3,5-dimethylphenyl)butane,2,2-bis(4-hydroxy-3,5-dipropylphenyl)propane,1,1-bis(4-hydroxyphenyl)cyclohexane, and1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane. Those compounds maybe used alone or in combination thereof. Of those,2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane,and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane are preferablyused. Of those, 2,2-bis(4-hydroxyphenyl)propane and1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane are particularlypreferably used in combination thereof.

Examples of the stretching method include lateral uniaxial stretching,fixed-end biaxial stretching, and sequential biaxial stretching. Thefixed-end biaxial stretching is specifically, for example, a methodincluding stretching the polymer film in its short direction (lateraldirection) while causing the film to travel in its lengthwise direction.The method may be apparently lateral uniaxial stretching. Obliquestretching may also be adopted. The adoption of the oblique stretchingcan provide an elongate stretched film having an alignment axis (slowaxis) at a predetermined angle with respect to its widthwise direction.

The thickness of the stretched film is typically from 5 μm to 80 μm,preferably from 15 μm to 60 μm, more preferably from 25 μm to 45 μm.

A-4. Second Retardation Layer (Retardation Layer Configured to Functionas λ/2 Plate)

As described above, the second retardation layer may function as a λ/2plate. The in-plane retardation Re(550) of such second retardation layeris preferably from 180 nm to 300 nm, more preferably from 210 nm to 280nm, most preferably from 230 nm to 240 nm. It is preferred that thesecond retardation layer typically have a refractive index ellipsoid ofnx>ny=nz. The Nz coefficient of the second retardation layer is, forexample, from 0.9 to 2, preferably from 1 to 1.5, more preferably from 1to 1.3.

The thickness of the second retardation layer may be set so that thelayer may most appropriately function as a λ/2 plate. In other words,the thickness may be set so that a desired in-plane retardation may beobtained. Specifically, the thickness is preferably from 0.5 μm to 5 μm,more preferably from 1 μm to 4 μm, most preferably from 1.5 μm to 3 μm.

Any appropriate material may be adopted as a material for the secondretardation layer as long as such characteristics as described above areobtained. A liquid crystal material is preferred, and a liquid crystalmaterial whose liquid crystal phase is a nematic phase (nematic liquidcrystal) is more preferred. The use of the liquid crystal material canmake a difference between the nx and ny of the second retardation layerto be obtained much larger than that of a non-liquid crystal material.As a result, the thickness of the second retardation layer for obtaininga desired in-plane retardation can be markedly reduced. For example, aliquid crystal polymer or a liquid crystal monomer may be used as suchliquid crystal material. The mechanism via which the liquidcrystallinity of the liquid crystal material is expressed may be any oneof a lyotropic mechanism and a thermotropic mechanism. In addition, thealignment state of the liquid crystal material is preferably homogeneousalignment. In addition, the resin forming the polymer film may be usedas the material for the second retardation layer.

The second retardation layer may show such a reverse wavelengthdispersion characteristic that its retardation value increases inaccordance with an increase in wavelength of measurement light, may showsuch a positive wavelength dispersion characteristic that theretardation value reduces in accordance with an increase in wavelengthof the measurement light, or may show such a flat wavelength dispersioncharacteristic that the retardation value remains substantiallyunchanged irrespective of the wavelength of the measurement light. Thelayer preferably shows a flat wavelength dispersion characteristic. Theadoption of a λ/2 plate having a flat wavelength dispersioncharacteristic can achieve an excellent antireflection characteristicand an excellent reflection hue in an oblique direction. The ratioRe(450)/Re(550) of the retardation layer is preferably from 0.99 to1.03, and the ratio Re(650)/Re(550) thereof is preferably from 0.98 to1.02.

A-5. Colored Layer

The colored layer contains one or more kinds of coloring materials. Inthe coloring material, the coloring material is typically present in amatrix.

As described above, the colored layer has an absorption peak in thewavelength band in the range of from 580 nm to 610 nm. The formation ofsuch colored layer can improve the antireflection function of thecircularly polarizing plate while suppressing a reduction in visiblelight transmittance (i.e., a reduction in brightness) thereof. Inaddition, when the wavelength of light to be absorbed by the layer isadjusted, a reflection hue can be made neutral, and hence a circularlypolarizing plate reduced in coloring can be obtained. The absorptionspectrum of the layer may be measured with a spectrophotometer(manufactured by Hitachi High-Technologies Corporation, product name:“U-4100”).

The ratio (A₅₄₅/A_(max)) of the absorbance A₅₄₅ of the peak of thecolored layer at a wavelength of 545 nm to the absorbance A_(max) of thehighest absorption peak of the colored layer at a wavelength of from 580nm to 610 nm is preferably 0.13 or less, more preferably 0.1 or less,still more preferably 0.08 or less, particularly preferably 0.05 orless. When a colored layer having a small absorbance at a wavelength of545 nm as described above is formed, a circularly polarizing plate thatcan contribute to the widening of the color gamut of an image displayapparatus by absorbing light that is not needed for color representationcan be obtained. In addition, the layer hardly absorbs light emittedfrom a light source whose wavelength is around 545 nm at which avisibility is high, and hence can be suppressed in brightness reduction.

In the colored layer, the half width of the absorption peak in thewavelength range of from 580 nm to 610 nm is preferably 35 nm or less,more preferably 30 nm or less, still more preferably 25 nm or less,particularly preferably 20 nm or less. When the half width falls withinsuch ranges, a circularly polarizing plate that can contribute to thewidening of the color gamut of an image display apparatus can beobtained.

In one embodiment, the colored layer is free of an absorption peak inthe range of from 530 nm to 570 nm. More specifically, the colored layeris free of an absorption peak having an absorbance of 0.1 or more in therange of from 530 nm to 570 nm. The formation of such colored layer canprovide a circularly polarizing plate that can contribute to thewidening of the color gamut of an image display apparatus.

In one embodiment, the colored layer further has an absorption peak in awavelength band in the range of from 440 nm to 510 nm. That is, in thisembodiment, the colored layer has absorption peaks in the wavelengthbands in the ranges of from 440 nm to 510 nm and from 580 nm to 610 nm.With such configuration, the color mixing of red light and green light,and that of green light and blue light can be satisfactorily prevented.When the circularly polarizing plate configured as described above isused as an antireflection film for an image display apparatus, the colorgamut of the image display apparatus can be widened, and hence brightand vivid image quality can be obtained. A colored layer having two ormore absorption peaks as described above may be obtained by using aplurality of kinds of coloring materials.

The transmittance of the colored layer at an absorption peak ispreferably from 0% to 80%, more preferably from 0% to 70%. When thetransmittance falls within such ranges, the above-mentioned effect ofthe present invention becomes more significant.

The visible light transmittance of the colored layer is preferably from30% to 90%, more preferably from 30% to 80%. When the visible lighttransmittance falls within such ranges, a circularly polarizing platethat can exhibit an antireflection function while being suppressed inbrightness reduction can be obtained.

The haze value of the colored layer is preferably 15% or less, morepreferably 10% or less, still more preferably 5% or less. When the hazevalue of the colored layer is set within such ranges, the depolarizationof circularly polarized light that has passed the first retardationlayer (and the second retardation layer) is prevented, and as a result,a circularly polarizing plate having an excellent antireflectioncharacteristic can be obtained. Although the haze value of the coloredlayer is preferably as small as possible, its lower limit is, forexample, 0.1%.

The thickness of the colored layer is preferably from 1 μm to 100 μm,more preferably from 2 μm to 30 μm.

A-5-1. Coloring Material

The colored layer contains, as a coloring material, a compound Xrepresented by the following general formula (I) or general formula(II). The compound X is a compound having an absorption peak in thewavelength band in the range of from 580 nm to 610 nm.

in the formula (I),

R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ each independently represent ahydrogen atom, a halogen atom, a substituted or unsubstituted alkylgroup having 1 or more and 20 or less carbon atoms, a substituentrepresented by the formula (a), or a substituent represented by theformula (b),

R₁ and R₂ form a saturated cyclic skeleton including 5 or 6 carbonatoms, and R₃, R₄, R₅, R₆, R₇, and R₈ each independently represent ahydrogen atom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b),

R₂ and R₃ form a saturated cyclic skeleton including 5 to 7 carbonatoms, and R₁, R₄, R₅, R₆, R₇, and R₈ each independently represent ahydrogen atom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b),

R₅ and R₆ form a saturated cyclic skeleton including 5 or 6 carbonatoms, and R₁, R₂, R₃, R₄, R₇, and R₈ each independently represent ahydrogen atom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b),

R₆ and R₇ form a saturated cyclic skeleton including 5 to 7 carbonatoms, and R₁, R₂, R₃, R₄, R₅, and R₈ each independently represent ahydrogen atom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b),

R₁ and R₂ form a saturated cyclic skeleton including 5 or 6 carbonatoms, R₅ and R₆ form a saturated cyclic skeleton including 5 or 6carbon atoms, and R₃, R₄, R₇, and R₈ each independently represent ahydrogen atom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b), or

R₂ and R₃ form a saturated cyclic skeleton including 5 to 7 carbonatoms, R₆ and R₇ form a saturated cyclic skeleton including 5 to 7carbon atoms, and R₁, R₄, R₅, and R₈ each independently represent ahydrogen atom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b); and

in the formula (II), R₄ and R₈ each independently represent a hydrogenatom, or a substituted or unsubstituted alkyl group having 1 or more and20 or less carbon atoms.

The saturated cyclic skeleton (number of carbon atoms: 5 or 6) formed soas to include R₁ and R₂, and the saturated cyclic skeleton (number ofcarbon atoms: 5 or 6) formed so as to include R₅ and R₆ may each have asubstituent. The substituent is, for example, an alkyl group having 1 to4 carbon atoms. In addition, the saturated cyclic skeleton (number ofcarbon atoms: 5 to 7) formed so as to include R₂ and R₃, and thesaturated cyclic skeleton (number of carbon atoms: 5 to 7) formed so asto include R₆ and R₇ may each have a substituent. The substituent is,for example, an alkyl group having 1 to 4 carbon atoms.

In one embodiment, R₄ and/or R₈ has a benzene ring or a naphthalene ringas a substituent.

Specific examples of the compound X represented by the formula (I) or(II) include compounds represented by the following general formulae(I-1) to (I-27) and (II-1). The absorption peak of the compound X isshown in each of the following tables. With regard to each of theformulae (I-1) to (I-23), an absorption peak obtained by measuring theabsorbance of a film formed of a resin composition prepared by mixingaliphatic polycarbonate with the compound X is shown, and with regard toeach of the formulae (I-24) to (I-27) and (II-1), an absorption peakobtained by measuring the absorbance of a film formed of a resincomposition prepared by mixing a polymethyl methacrylate resin with thecompound X is shown.

Absorption peak NO. Compound X (nm) I-1

596 nm (APC) I-2

595 nm (APC) I-3

582 nm (APC) I-4

585 nm (APC) I-5

585 nm (APC) I-6

575 nm (APC) I-7

585 nm (APC) I-8

587 nm (APC) I-9

587 nm (APC) I-10

588 nm (APC) I-11

588 nm (APC) I-12

589 nm (APC) I-13

592 nm (APC) I-14

591 nm (APC) I-15

595 nm (APC) I-16

595 nm (APC) I-17

596 nm (APC) I-18

614 nm (APC) I-19

581 nm (APC) I-20

591 nm (APC) I-21

593 nm (APC) I-22

594 nm (APC) I-23

594 nm (APC) I-24

592 nm I-25

593 nm I-26

594 nm I-27

594 nm II-1

597 nm

The content of the compound X is preferably from 0.01 part by weight to50 parts by weight, more preferably from 0.05 part by weight to 10 partsby weight, still more preferably from 0.1 part by weight to 5 parts byweight, particularly preferably from 0.1 part by weight to 1 part byweight with respect to 100 parts by weight of a matrix material.

The colored layer may further contain a compound having an absorptionpeak in the wavelength band in the range of from 440 nm to 510 nm. Forexample, an anthraquinone-based, oxime-based, naphthoquinone-based,quinizarin-based, oxonol-based, azo-based, xanthene-based, orphthalocyanine-based compound (dye) is used as such compound.

The content of the compound having an absorption peak in the wavelengthband in the range of from 440 nm to 510 nm is preferably from 0.01 partby weight to 50 parts by weight, more preferably from 0.01 part byweight to 25 parts by weight with respect to 100 parts by weight of thematrix material.

A-5-2. Matrix

The matrix may be a pressure-sensitive adhesive, or may be a resin film.The matrix is preferably a pressure-sensitive adhesive.

When the matrix is a pressure-sensitive adhesive, any appropriatepressure-sensitive adhesive may be used as the pressure-sensitiveadhesive. The pressure-sensitive adhesive preferably has transparencyand optical isotropy. Specific examples of the pressure-sensitiveadhesive include a rubber-based pressure-sensitive adhesive, an acrylicpressure-sensitive adhesive, a silicone-based pressure-sensitiveadhesive, an epoxy-based pressure-sensitive adhesive, and acellulose-based pressure-sensitive adhesive. Of those, a rubber-basedpressure-sensitive adhesive or an acrylic pressure-sensitive adhesive ispreferred.

A rubber-based polymer serving as the rubber-based pressure-sensitiveadhesive is a polymer showing rubber elasticity in a temperature regionaround room temperature. Preferred examples of the rubber-based polymer(A) include a styrene-based thermoplastic elastomer (A1), anisobutylene-based polymer (A2), and a combination thereof.

Examples of the styrene-based thermoplastic elastomer (A1) may includestyrene-based block copolymers, such as astyrene-ethylene-butylene-styrene block copolymer (SEBS), astyrene-isoprene-styrene block copolymer (SIS), astyrene-butadiene-styrene block copolymer (SBS), astyrene-ethylene-propylene-styrene block copolymer (SEPS, a hydrogenatedproduct of SIS), a styrene-ethylene-propylene block copolymer (SEP, ahydrogenated product of a styrene-isoprene block copolymer), astyrene-isobutylene-styrene block copolymer (SIBS), and astyrene-butadiene rubber (SBR). Of those, astyrene-ethylene-propylene-styrene block copolymer (SEPS, a hydrogenatedproduct of SIS), a styrene-ethylene-butylene-styrene block copolymer(SEBS), and a styrene-isobutylene-styrene block copolymer (SIBS) arepreferred because the copolymers each have polystyrene blocks at bothends of a molecule thereof and have a high cohesive force as a polymer.A commercial product may be used as the styrene-based thermoplasticelastomer (A1). Specific examples of the commercial product includeSEPTON and HYBRAR manufactured by Kuraray Co., Ltd., Tuftec manufacturedby Asahi Kasei Chemicals Corporation, and SIBSTAR manufactured by KanekaCorporation.

The weight-average molecular weight of the styrene-based thermoplasticelastomer (A1) is preferably from about 50,000 to about 500,000, morepreferably from about 50,000 to about 300,000, still more preferablyfrom about 50,000 to about 250,000. The weight-average molecular weightof the styrene-based thermoplastic elastomer (A1) preferably fallswithin such ranges because both of the cohesive force andviscoelasticity of the polymer can be achieved.

A styrene content in the styrene-based thermoplastic elastomer (A1) ispreferably from about 5 wt % to about 70 wt %, more preferably fromabout 5 wt % to about 40 wt %, still more preferably from about 10 wt %to about 20 wt %. The styrene content in the styrene-based thermoplasticelastomer (A1) preferably falls within such ranges becauseviscoelasticity based on a soft segment can be secured while a cohesiveforce based on a styrene moiety is maintained.

Examples of the isobutylene-based polymer (A2) may include polymers eachincluding isobutylene as a constituent monomer and having aweight-average molecular weight (Mw) of preferably 500,000 or more. Theisobutylene-based polymer (A2) may be a homopolymer of isobutylene(polyisobutylene, PIB) or may be a copolymer including isobutylene asamain monomer (i.e., a copolymer obtained by copolymerizing isobutyleneat a ratio of more than 50 mol %). Examples of such copolymer mayinclude a copolymer of isobutylene and normal butylene, a copolymer ofisobutylene and isoprene (e.g., a butyl rubber, such as a regular butylrubber, a chlorinated butyl rubber, a brominated butyl rubber, or apartially cross-linked butyl rubber), and vulcanized products andmodified products thereof (e.g., a product modified with a functionalgroup, such as a hydroxyl group, a carboxyl group, an amino group, or anepoxy group). Of those, polyisobutylene (PIB) is preferred because thepolyisobutylene is free of a double bond in its main chain, and isexcellent in weatherability. A commercial product may be used as theisobutylene-based polymer (A2). The commercial product is specifically,for example, OPPANOL manufactured by BASF.

The weight-average molecular weight (Mw) of the isobutylene-basedpolymer (A2) is preferably 500,000 or more, more preferably 600,000 ormore, still more preferably 700,000 or more. In addition, the upperlimit of the weight-average molecular weight (Mw) is preferably5,000,000 or less, more preferably 3,000,000 or less, still morepreferably 2,000,000 or less. When the weight-average molecular weightof the isobutylene-based polymer (A2) is set to 500,000 or more, apressure-sensitive adhesive that is more excellent in durability at thetime of its high-temperature storage can be obtained.

The content of the rubber-based polymer (A) in the pressure-sensitiveadhesive is preferably 30 wt % or more, more preferably 40 wt % or more,still more preferably 50 wt % or more, particularly preferably 60 wt %or more in the total solid content of the pressure-sensitive adhesive.The upper limit of the content of the rubber-based polymer is preferably95 wt % or less, more preferably 90 wt % or less.

In the rubber-based pressure-sensitive adhesive, the rubber-basedpolymer (A) and any other rubber-based polymer may be used incombination. Specific examples of the other rubber-based polymerinclude: a butyl rubber (IIR), a butadiene rubber (BR), anacrylonitrile-butadiene rubber (NBR), EPR (binary ethylene-propylenerubber), EPT (ternary ethylene-propylene rubber), an acrylic rubber, aurethane rubber, and a polyurethane-based thermoplastic elastomer; apolyester-based thermoplastic elastomer; and a blend-based thermoplasticelastomer, such as a polymer blend of polypropylene and EPT (ternaryethylene-propylene rubber). The compounding amount of the otherrubber-based polymer is preferably about 10 parts by weight or less withrespect to 100 parts by weight of the rubber-based polymer (A).

The acrylic polymer of the acrylic pressure-sensitive adhesive typicallycontains an alkyl (meth)acrylate as a main component, and may contain anaromatic ring-containing (meth)acrylate, an amide group-containingmonomer, a carboxyl group-containing monomer, and/or a hydroxylgroup-containing monomer as a copolymerization component in accordancewith a purpose. The term “(meth)acrylate” as used herein means anacrylate and/or a methacrylate. The alkyl (meth)acrylate may be, forexample, an alkyl (meth)acrylate having a linear or branched alkyl grouphaving 1 to 18 carbon atoms. The aromatic ring-containing (meth)acrylateis a compound containing an aromatic ring structure in its structure andcontaining a (meth)acryloyl group. The aromatic ring is, for example, abenzene ring, a naphthalene ring, or a biphenyl ring. The aromaticring-containing (meth)acrylate satisfies durability and can alleviatedisplay unevenness due to a white void of the peripheral portion of animage display apparatus. The amide group-containing monomer is acompound containing an amide group in its structure and containing apolymerizable unsaturated double bond, such as a (meth)acryloyl group ora vinyl group. The carboxyl group-containing monomer is a compoundcontaining a carboxyl group in its structure and containing apolymerizable unsaturated double bond, such as a (meth)acryloyl group ora vinyl group. The hydroxyl group-containing monomer is a compoundcontaining a hydroxyl group in its structure and containing apolymerizable unsaturated double bond, such as a (meth)acryloyl group ora vinyl group. Details about the acrylic pressure-sensitive adhesive aredescribed in, for example, JP 2015-199942 A, the description of which isincorporated herein by reference.

When the matrix is a resin film, any appropriate resin may be used as aresin forming the resin film. Specifically, the resin may be athermoplastic resin, may be a thermosetting resin, or may be an activeenergy ray-curable resin. Examples of the active energy ray-curableresin include an electron beam-curable resin, a UV-curable resin, and avisible light-curable resin. Specific examples of the resin include anepoxy, a (meth)acrylate (e.g., methyl methacrylate or butyl acrylate),norbornene, polyethylene, poly(vinyl butyral), poly(vinyl acetate),polyurea, polyurethane, aminosilicone (AMS), polyphenylmethylsiloxane, apolyphenylalkylsiloxane, polydiphenylsiloxane, a polydialkylsiloxane,silsesquioxane, silicone fluoride, vinyl- and hydride-substitutedsilicones, a styrene-based polymer (e.g., polystyrene, aminopolystyrene(APS), poly(acrylonitrile ethylene styrene) (AES)), a polymer havingcross-linked with a di functional monomer (e.g., divinylbenzene), apolyester-based polymer (e.g., polyethylene terephthalate), acellulose-based polymer (e.g., triacetyl cellulose), a vinylchloride-based polymer, an amide-based polymer, an imide-based polymer,a vinyl alcohol-based polymer, an epoxy-based polymer, a silicone-basedpolymer, and an acrylic urethane-based polymer. Those resins may be usedalone or in combination thereof (e.g., a blend or a copolymer). Thoseresins may each be subjected to a treatment, such as stretching,heating, or pressurization, after forming a film. Of those, athermosetting resin or a UV-curable resin is preferred, and athermosetting resin is more preferred.

B. Image Display Apparatus

An image display apparatus of the present invention includes an imagedisplay panel and the circularly polarizing plate. Examples of the imagedisplay panel include a liquid crystal display panel and an organic ELpanel. The circularly polarizing plate is arranged on the viewer side ofthe image display panel, and is arranged so that the colored layer maybe on an image display panel side, and the polarizer may be on theviewer side.

An image display panel having a high reflectance (e.g., an image displaypanel that includes, for example, a member formed of a metal or a membercontaining a metal, and that has a high reflectance) is suitably used asthe image display panel. The circularlypolarizingplate of the presentinvention has an excellent antireflection characteristic and anexcellent hue-adjusting function. Accordingly, even in an image displayapparatus including the image display panel having a high reflectance,the influence of ambient light reflection can be effectively reduced.The visible light reflectance of the image display panel is, forexample, 20% or more, preferably from 40% to 99%.

EXAMPLES

Now, the present invention is specifically described byway of Examples.However, the present invention is by no means limited by these Examples.Methods of measuring the respective characteristics are as describedbelow.

[Evaluation]

(1) Measurement of Absorption Spectrum

A colored layer was dissolved in ethyl acetate to prepare an evaluationsample.

The absorption spectrum of the evaluation sample was measured with aspectrophotometer (manufacturedby Hitachi High-Technologies Corporation,product name: “U-4100”).

(2) Measurement of Color Gamut

A circularly polarizing plate was arranged on the viewer side of iPadmanufactured by Apple Inc. so that its colored layer was on an iPadside. Thus, an evaluation sample was obtained.

In a dark room, chromaticities at the time of the red display of theevaluation sample, at the time of the blue display thereof, and at thetime of the green display thereof were measured with a luminancecolorimeter (manufactured by Topcon Technohouse Corporation, productname: “SR-UL1”). A DCI ratio (area B/area A) was calculated from thearea A of a triangle formed by connecting the chromaticity coordinatesof the respective colors, and the area B of a region where the triangleformed by connecting the chromaticity coordinates of the respectivecolors and the color gamut standard of DCI overlapped each other.

(3) Measurement of Reflectance of Circularly Polarizing Plate

A circularly polarizing plate was bonded to a reflective plate(manufactured by Toray Advanced Film Co., Ltd., product name: “CERAPEELDMS-X42”, total light reflectance: 86%) so that its colored layer was ona reflective plate side. Thus, an evaluation sample was produced. Thetotal light reflectance of the evaluation sample was measured withCM2600-d (manufactured by Konica Minolta, Inc.).

(4) Δab

The reflection hue (L*a*b* colorimetric system) of the evaluation sampleproduced in the (3) was measured with CM2600-d (manufactured by KonicaMinolta, Inc.), and the Lab thereof was determined from the equation“Δab=(a²+b²)^(1/2)”.

Example 1 (i) Production of Retardation Layer (λ/4 Plate)

Polymerization was performed by using a batch polymerization apparatusformed of two vertical reactors each including a stirring blade and areflux condenser controlled to 100° C.9,9-[4-(2-Hydroxyethoxy)phenyl]fluorene (BHEPF), isosorbide (ISB),diethylene glycol (DEG), diphenyl carbonate (DPC), and magnesium acetatetetrahydrate were loaded into a first reactor so that a molar ratio“BHEPF/ISB/DEG/DPC/magnesium acetate” became0.348/0.490/0.162/1.005/1.00×10⁻⁵. After air in the reactor had beensufficiently purged with nitrogen (oxygen concentration: from 0.0005 vol% to 0.001 vol %), a temperature in the reactor was warmed with aheating medium, and stirring was started at the time point when theinternal temperature became 100° C. 40 Minutes after the start of thetemperature increase, the internal temperature was caused to reach 220°C., and such control that the temperature was held was performed.Simultaneously with the control, the reduction of a pressure in thereactor was started, and the pressure was set to 13.3 kPa in 90 minutesafter the temperature had reached 220° C. Phenol vapor produced as aby-product of the polymerization reaction was introduced into the refluxcondenser at 100° C. A monomer component present in a trace amount inthe phenol vapor was returned to the reactor, and the phenol vapor thatdid not condense was introduced into a condenser at 45° C. andcollected.

Nitrogen was introduced into the first reactor to return the pressure toatmospheric pressure once. After that, the oligomerized reaction liquidin the first reactor was transferred to a second reactor. Next, theincrease of a temperature in the second reactor and the reduction of apressure therein were started, and the internal temperature and thepressure were set to 240° C. and 0.2 kPa, respectively in 50 minutes.After that, polymerization was advanced until predetermined stirringpower was obtained. At the time point when the predetermined power wasachieved, nitrogen was introduced into the reactor to return thepressure to atmospheric pressure. The reaction liquid was extracted inthe form of a strand, and was pelletized with a rotary cutter to providea polycarbonate resin having a copolymerization composition“BHEPF/ISB/DEG” of 34.8/49.0/16.2 [mol %]. The polycarbonate resin had areduced viscosity of 0.430 dL/g and a glass transition temperature of128° C.

The resultant polycarbonate resin (10 kg) was dissolved in methylenechloride (73 kg) to prepare an application liquid. Next, the applicationliquid was directly applied onto a shrinkable film (longitudinallyuniaxially stretched polypropylene film, manufactured by Tokyo PrintingInk Mfg Co., Ltd., product name: “NOBLEN”). The applied film was driedat a drying temperature of 30° C. for 5 minutes and at a dryingtemperature of 80° C. for 5 minutes to form a laminate having theconfiguration “shrinkable film/birefringent layer”. The resultantlaminate was stretched with a simultaneous biaxial stretching machine ata stretching temperature of 155° C. in its MD direction at a shrinkageratio of 0.80 times and in its TD direction at a stretching ratio of 1.3times to form a retardation film A on the shrinkable film. Next, theretardation film was peeled from the shrinkable film. The retardationfilm A had a thickness of 60.0 μm, an Re(550) of 140 nm, an Nzcoefficient of 0.5, and a ratio Re(450)/Re(550) of 0.89. The retardationfilm A was adopted as a retardation layer (λ/4 plate).

(ii) Production of Polarizer

An elongate roll of a polyvinyl alcohol (PVA)-based resin film having athickness of 30 μm (manufactured by Kuraray Co., Ltd., product name:“PE3000”) was uniaxially stretched with a roll stretching machine in itslengthwise direction at a stretching ratio of 5.9 times in thelengthwise direction. Simultaneously with the stretching, the film wassubjected to swelling, dyeing, cross-linking, and washing treatments,and was finally subjected to a drying treatment to produce a polarizerhaving a thickness of 12 μm.

Specifically, in the swelling treatment, the film was stretched at astretching ratio of 2.2 times while being treated with pure water at 20°C. Next, in the dyeing treatment, the film was stretched at a stretchingratio of 1.4 times while being treated in an aqueous solution at 30° C.containing iodine and potassium iodide at a weight ratio of 1:7 in whichan iodine concentration was adjusted so that the single layertransmittance of the polarizer to be obtained became 45.0%. Further, inthe cross-linking treatment, a two-stage cross-linking treatment wasadopted, and in a first-stage cross-linking treatment, the film wasstretched at a stretching ratio of 1.2 times while being treated in anaqueous solution at 40° C. having dissolved therein boric acid andpotassium iodide. The boric acid content of the aqueous solution in thefirst-stage cross-linking treatment was set to 5.0 wt %, and thepotassium iodide content thereof was set to 3.0 wt %. In a second-stagecross-linking treatment, the film was stretched at a stretching ratio of1.6 times while being treated in an aqueous solution at 65° C. havingdissolved therein boric acid and potassium iodide. The boric acidcontent of the aqueous solution in the second-stage cross-linkingtreatment was set to 4.3 wt %, and the potassium iodide content thereofwas set to 5.0 wt %. In addition, in the washing treatment, the film wastreated with a potassium iodide aqueous solution at 20° C. The potassiumiodide content of the aqueous solution in the washing treatment was setto 2.6 wt %. Finally, in the drying treatment, the film was dried at 70°C. for 5 minutes to provide the polarizer.

(iii) Production of Polarizing Plate A

AHC-TAC film (thickness: 32 μm, corresponding to a protective film)including a hard coat (HC) layer formed on one surface of a TAC film bya hard coat treatment was bonded to one side of the polarizer via apolyvinyl alcohol-based adhesive through a roll-to-roll process. Thus,an elongate polarizing plate A having the configuration “protectivefilm/polarizer” was obtained.

(iv) Production of Polarizing Plate A with Retardation Layer

The polarizing plate and the retardation layer obtained in the foregoingwere each cut into a predetermined size, and the polarizer surface ofthe polarizing plate and the retardation layer were bonded to each othervia an acrylic pressure-sensitive adhesive. Thus, a polarizing plate Awith a retardation layer having the configuration “protectivefilm/polarizer/retardation layer (λ/4 plate)” was obtained. Theretardation layer was cut so that an angle formed by the absorption axisof the polarizer and the slow axis of the retardation layer became 45°at the time of the bonding of the polarizing plate and the retardationlayer.

(v) Formation of Colored Layer

A coloring matter-containing pressure-sensitive adhesive containing 0.3part by weight of a radical generator (benzoyl peroxide, manufactured byNippon Oil & Fats Co., Ltd., product name: “NYPER BMT”), 1 part byweight of an isocyanate-based cross-linking agent (manufactured by TosohCorporation, product name: “CORONATE L”), 0.25 part by weight of asquaraine compound represented by the following general formula (I-20),and 0.2 part by weight of a phenol-based antioxidant (manufactured byBASF Japan Ltd., product name: “IRGANOX 1010”) with respect to 100 partsby weight of an acrylic polymer obtained by copolymerizing n-butylacrylate and a hydroxy group-containing monomer was produced. Thepressure-sensitive adhesive was applied onto a PET substrate(manufacturedbyMitsubishi Plastics, Inc., product name: “MRF38CK”),which had been subjected to a treatment for facilitating the peeling ofthe pressure-sensitive adhesive, with an applicator so as to have athickness of 20 μm, and the adhesive was dried at 155° C. for 2 minutes.After that, the pressure-sensitive adhesive sample was removed, and thepressure-sensitive adhesive surface was bonded to the retardation layerside of the polarizing plate with a retardation layer. Thus, a coloredlayer (absorption maximum wavelength: 594 nm) was formed.

The squaraine compound represented by the general formula (I-20) wassynthesized by the following method.

<Synthesis of Squaraine Compound>

1-Phenyl-1,4,5,6-tetrahydrocyclopenta[b]pyrrole was synthesized by amethod described in “M. Beller et. al., J. Am. Chem. Soc., 2013,135(30), 11384-11388”.

300 Milligrams of 1-phenyl-1,4,5,6-tetrahydrocyclopenta[b]pyrrole and 80mg of squaric acid were mixed in 5 mL of ethanol, and the mixture wasstirred at 80° C. for 2 hours. After that, the mixture was cooled toroom temperature, and the product was filtered out. The product that hadbeen filtered out was washed with ethanol, and was dried under reducedpressure at 70° C. to provide 197 mg of a squaraine compound. Further,the compound was purified by silica gel chromatography to provide 120 mgof a squaraine compound.

A circularly polarizing plate including the protective film, thepolarizer, the retardation layer (λ/4 plate), and the colored layer wasobtained as described above. The resultant circularly polarizing platewas subjected to the evaluations (2) to (4). The results are shown inTable 1.

Comparative Example 1

(i) Production of Polarizing Plate A with Retardation Layer

The polarizing plate A with a retardation layer was obtained in the samemanner as in Example 1.

(ii) Formation of Colored Layer

A circularly polarizing plate including the protective film, thepolarizer, the retardation layer (λ/4 plate), and a colored layer(absorption maximum wavelength: 595 nm) was obtained in the same manneras in Example 1 except that 0.25 part by weight of a porphyrin-basedcoloring matter (manufactured by Yamamoto Chemicals, Inc., product name:“PD-320”) was used instead of 0.25 part by weight of the squarainecompound represented by the general formula (I-20). The resultantcircularly polarizing plate was subjected to the evaluations (2) to (4).The results are shown in Table 1.

Comparative Example 2

A circularly polarizing plate was obtained in the same manner as inExample 1 except that the coloring matter (squaraine compound) was notincorporated into the pressure-sensitive adhesive forming the coloredlayer (i.e., a pressure-sensitive adhesive layer was formed instead ofthe colored layer). The resultant circularly polarizing plate wassubjected to the evaluations (2) to (4). The results are shown in Table1.

TABLE 1 Color gamut Reflectance (DCI ratio) Coloring matter (%) Δab (%)Example 1 Squaraine compound 2.39 22.3 57 (formula (II)) ComparativePorphyrin-based 2.49 26.7 55 Example 1 coloring matter Comparative —2.66 25.1 51 Example 2

As is apparent from Table 1, according to the present invention, acircularly polarizing plate that is excellent in antireflectioncharacteristic, that can output light having a small Lab and a neutralhue, and that can widen the color gamut of an image display apparatuscan be obtained.

INDUSTRIAL APPLICABILITY

The circularly polarizing plate of the present invention is suitablyused in an image display apparatus, such as a liquid crystal displayapparatus.

REFERENCE SIGNS LIST

-   -   10 polarizer    -   20 a retardation layer    -   30 colored layer    -   100 circularly polarizing plate

1. A circularly polarizing plate, comprising in the stated order: apolarizer; a retardation layer “a” configured to function as a λ/4plate; and a colored layer, wherein an angle formed by an absorptionaxis of the polarizer and a slow axis of the retardation layer “a” isfrom 35° to 55°, wherein the colored layer has an absorption peak in awavelength band in a range of from 580 nm to 610 nm, and wherein thecolored layer contains a compound X represented by the following generalformula (I) or general formula (II):

in the formula (I), R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ eachindependently represent a hydrogen atom, a halogen atom, a substitutedor unsubstituted alkyl group having 1 or more and 20 or less carbonatoms, a substituent represented by the formula (a), or a substituentrepresented by the formula (b), R₁ and R₂ form a saturated cyclicskeleton including 5 or 6 carbon atoms, and R₃, R₄, R₅, R₆, R₇, and R₈each independently represent a hydrogen atom, a halogen atom, which ispreferably Cl, a substituted or unsubstituted alkyl group having 1 ormore and 20 or less carbon atoms, a substituent represented by theformula (a), or a substituent represented by the formula (b), R₂ and R₃form a saturated cyclic skeleton including 5 to 7 carbon atoms, and R₁,R₄, R₅, R₆, R₇, and R₈ each independently represent a hydrogen atom, ahalogen atom, which is preferably Cl, a substituted or unsubstitutedalkyl group having 1 or more and 20 or less carbon atoms, a substituentrepresented by the formula (a), or a substituent represented by theformula (b), R₅ and R₆ form a saturated cyclic skeleton including 5 or 6carbon atoms, and R₁, R₂, R₃, R₄, R₇, and R₈ each independentlyrepresent a hydrogen atom, a halogen atom, which is preferably Cl, asubstituted or unsubstituted alkyl group having 1 or more and 20 or lesscarbon atoms, a substituent represented by the formula (a), or asubstituent represented by the formula (b), R₆ and R₇ form a saturatedcyclic skeleton including 5 to 7 carbon atoms, and R₁, R₂, R₃, R₄, R₅,and R₈ each independently represent a hydrogen atom, a halogen atom,which is preferably Cl, a substituted or unsubstituted alkyl grouphaving 1 or more and 20 or less carbon atoms, a substituent representedby the formula (a), or a substituent represented by the formula (b), R₁and R₂ form a saturated cyclic skeleton including 5 or 6 carbon atoms,R₅ and R₇ form a saturated cyclic skeleton including 5 or 6 carbonatoms, and R₃, R₄, R₇, and R₈ each independently represent a hydrogenatom, a halogen atom, which is preferably Cl, a substituted orunsubstituted alkyl group having 1 or more and 20 or less carbon atoms,a substituent represented by the formula (a), or a substituentrepresented by the formula (b), or R₂ and R₃ form a saturated cyclicskeleton including 5 to 7 carbon atoms, R₅ and R₇ form a saturatedcyclic skeleton including 5 to 7 carbon atoms, and R₁, R₄, R₅, and R₈each independently represent a hydrogen atom, a halogen atom, which ispreferably Cl, a substituted or unsubstituted alkyl group having 1 ormore and 20 or less carbon atoms, a substituent represented by theformula (a), or a substituent represented by the formula (b); and in theformula (II), R₄ and R₈ each independently represent a hydrogen atom, ora substituted or unsubstituted alkyl group having 1 or more and 20 orless carbon atoms.
 2. The circularly polarizing plate according to claim1, wherein a laminate including the polarizer and the colored layer hasa polarization degree of 99.9% or more.
 3. The circularly polarizingplate according to claim 1, further comprising a retardation layer “b”configured to function as a λ/2 plate between the polarizer and theretardation layer “a” configured to function as a λ/4 plate, wherein theangle formed by the absorption axis of the polarizer and the slow axisof the retardation layer “a” is from 65° to 85°, and wherein an angleformed by the absorption axis of the polarizer and a slow axis of theretardation layer “b” is from 10° to 20°.
 4. The circularly polarizingplate according to claim 1, wherein the colored layer further has anabsorption peak in a wavelength band in a range of from 440 nm to 510nm.
 5. The circularly polarizing plate according to claim 1, wherein theretardation layer “a” configured to function as a λ/4 plate has a ratioRe(450)/Re(550) of 0.5 or more and less than 1.0, and wherein theretardation layer “a” has an Nz coefficient of from 0.3 to 0.7.
 6. Animage display apparatus, comprising the circularly polarizing plate ofclaim
 1. 7. The image display apparatus according to claim 6, furthercomprising an image display panel, wherein the image display panel has avisible light reflectance of 20% or more.